This looks like a useful tool, Medusa Power Analyzer Plus [link]http://www.hobby-lobby.com/bataccy.htm[/link]
Steve Maxwell

Got one, works fine. Still haven't had a chance to use the computer interface though.

I personally use the Micrologger from Eagletree Systems

http://www.eagletreesystems.com/micropower/micro.htm

With the temp and RMP sensor its pretty sweet. It was very useful the first 3 flights on a new plane. I could see exactly how it was handling in the air.